Integrated circuits are widely used for consumer, commercial and other applications. As is well known to those having skill in the art, an integrated circuit may include a large number of active devices, such as transistors, on an integrated circuit substrate. As the integration density of integrated circuit devices continues to increase, the number and/or complexity of processing steps may increase, and the performance of the individual devices may decrease. This increase in fabrication complexity may manifest itself in an increase in the number of masks that are used to define various regions in the integrated circuit.
One technique that has been used in attempts to improve the performance of n-channel field effect transistors (also referred to as NFETs) is the addition of stress in the NFET channel using a stress-generating material. The stress-generating material is generally a nitride material such as silicon nitride. When coated on an NFET device, the stress-generating material can induce stress in the NFET channel, which can increase mobility in the NFET channel. The stress may be memorized in the NFET channel by annealing the integrated circuit having the stress-generating layer thereon, so that the stress that is induced in the channel is “memorized” or rendered permanent in the channel. The stress-generating layer may then be removed.
Conventional field effect transistor fabrication processes may employ a first mask for source/drain implantation in an NFET, a second mask for source/drain implantation in a p-channel field effect transistor (PFET), and yet another mask to define a nitride stress-generating layer for the NFET. Unfortunately, the number of masks that are used may impact the cost, fabrication time and/or reliability of the integrated circuit. Moreover, in fabricating these devices, when a photoresist is etched to form one or more of these masks, the etched photoresist may react with the silicon nitride stress-generating layer and may produce contamination in the nitride stress-generating layer. This contamination is also referred to as “resist footing”, “nitride contamination” and/or “resist scum”.